Fiber optic substrates are comprised of one or more optical fibers grouped together in a ribbon or panel substrate configuration. Typically, the ribbon or panel substrate is about 0.01 to 0.03 inches thick. If one or more surfaces of the substrate are marred or abraded and a light source is applied to one end of the marred substrate, light will emit from the marred area. Accordingly, such a substrate may be marred to create a specific illumination pattern which can be effectively used to backlight a variety of displays. Increased surface marring also results in increased light emission. Accordingly, light intensity can also be varied along the length of the substrate by varied marring.
Previously, marring of fiber optic substrates was achieved by stamping the substrate with a roughened plate. In particular, a substrate would be placed on a cushion and a stamp having a covering, such as emery paper, would be pressed against the substrate to deform its surface. To increase the amount of surface marring along the substrate, the cushion was placed on a plate having a particular profile. For example, placing the cushion on a plate having an uprising surface, then stamping the substrate against the cushion, would result in minimal marring at the low end of the plate and greater marring at the high end of the plate. This marring pattern was particularly desirable when a single light source was to be applied at one end of the marred substrate. The result would be uniform lighting along the device due to the slight marring near the light source and the progressively greater marring as the distance from the light source increased. A symmetrically curved plate was also used wherein the greatest surface marring occurred at the middle of the substrate. Such a device provided uniform illumination when light sources were placed at both ends of the device. For further details, see U.S. Pat. No. 4,929,169 to Fujigaki et al. entitled Working Equipment For Roughening The Side Of Optical Fiber.
The stamping method described above has a number of disadvantages. One problem is that the length of substrate to be treated at one time is limited by the size of the stamp. Different sized stamps may be used, but larger stamps would obviously require more force to achieve the desired pressure profile against the cushion and plate. Furthermore, as the size of the stamp increases, it becomes more difficult to accurately apply the different simultaneous pressures required to produce a desired marring pattern along the substrate due to the larger cross sectional area of the plate. An additional problem is the necessity to change plates on the apparatus whenever a different marring pattern is desired.
Accordingly, a need has arisen for an apparatus that permits marring of substrates having different lengths or that require different marring patterns without interrupting operation of the apparatus to substitute suitable parts. It is also desirable that such an apparatus be capable of gradually and accurately altering the pressure profile applied to the substrate, again without interrupting operation of the apparatus.